Heretofore, synthetic resins, such as polyamide resin, fluororesin, polyester resin and polyolefin resin, e.g. ultra high molecular weight polyethylene, are widely used as materials of fishing lines, in view of requirements with respect to processability and mechanical properties such as strength. In particular, polyamide resin is especially commonly used as a material of fishing lines because it is flexible and highly resistant to abrasion and also because highly visible lines can be obtained easily since it can be dyed easily.
Polyamide resin is a resin which is originally excellent in abrasion resistance. In use of a fishing line made of a polyamide resin, however, it has been impossible to prevent the fishing line from being damaged due to so-called sea floor abrasion or rock abrasion, which are abrasion with rocks or the like on the bottom of the water and there has been a risk of breakage of the line. Therefore, for fishing lines made of polyamide resin, further improvement in abrasion resistance is required.
As means for improving abrasion resistance, 1) a method of applying or fixing an abrasion resistance modifier to the surface of a fishing line fiber and 2) a method of mixing an abrasion resistance modifier in the raw material resin of fishing lines have been proposed.
As an example of the method 1), a fishing line made of nylon coated with a fluorine-containing resin is disclosed in Patent Document 1. It is reported to be excellent in slipping property, antifouling property and abrasion resistance. Patent Document 2 discloses a fishing line composed of a polyamide monofilament having a surface provided with amino-modified silicone oil. This is reported to be resistant to damage due to abrasion with rocks or the like. Both of the fishing lines, however, are not sufficient in adhesion between a coating layer and a polyamide resin and tend to suffer from delamination or falling off due to repeated use. In practical use in fishing, the effects often disappear only in short-time use, for example, almost one-day use. It therefore is difficult to say that the durability of abrasion resisting effect is sufficient.
As an example of the method 2), Patent Document 3 discloses a fishing line made of a monofilament obtained by mixing a modified resin composed of a fluorine-containing resin and/or an organic silicon-based resin with nylon resin and then molding. It is reported to be excellent in slipping property, antifouling property and abrasion resistance. In Examples of Patent Document 3, an example of incorporation of polydimethylsilicone as an organic silicon-based resin is disclosed. The incorporation amount thereof, however, is just 0.05 parts by weight per 100 parts by weight of the nylon resin. No description was made to the molecular weight of the silicone blended.
As disclosed in Patent Document 3, the method in which silicone is kneaded into a nylon monofilament can improve the durability of the effect of improving abrasion resistance more than the method in which silicone is coated on the surface. However, kneaded silicone having a number average molecular weight less than 100,000 tends to bleed out to the surface of fiber. Therefore, the durability of abrasion resisting effect is not sufficient yet. Moreover, silicone having a number average molecular weight less than 100,000 has low viscosities at high temperatures. Therefore, in the case of kneading and melt-spinning with a polyamide at a high temperature, increase in the addition amount thereof will cause variation in fiber diameter or breakage of strands, resulting in remarkable decrease in spinnability. It, therefore, is difficult to conduct stable production in an industrial scale. Furthermore, in the case of increasing the addition amount of the silicone having a number average molecular weight less than 100,000, mechanical properties, such as tensile strength and knot strength, are also deteriorated remarkably, and no fishing lines having strength sufficient enough for practical use have been obtained.    Patent Document 1: Japanese Unexamined Patent Publication No. 60-224885    Patent Document 2: Japanese Unexamined Patent Publication No. 4-4832    Patent Document 3: Japanese Unexamined Patent Publication No. 2-269877